PCR as a new identification method of Xanthomonas campestris pv. campestris on Brassica spp. seed

摘要

The efficiency of the PCR technique for the identification of Xanthomonas campestris pv. campestris (Xcc) on Brassica spp. seed was compared to the pathogenicity test described in ISTA Seed Health Method 7-019 in a peer validation study organized by the International Seed Health Initiative for Vegetables. Four laboratories from the Netherlands arid France together tested 1472 suspect bacteria isolates of X. campestris pathovars by conducting in parallel a PCR and a pathogenicity test. Xcc was identified using the DLH primer sets by Berg et al. (2005) and the Zup primer sets by Rijlaarsdam et al. (2004), and the results of the PCR and pathogenicity test were summarized and compared. There is a negligible risk of a false-positive PCR result for Xcc, caused by primer sets target-irig X. campestris pv. incanae. It is highly unlikely that X. campestris pv. incanae isolates are present on cultivated Brassica spp. seeds. The study showed comparable results for the PCR and pathogenicity tests for 97.21% ofthe total of suspect isolates. Compared to the pathogenicity test, the PCR produced a false-negative result in only 0.4P/o of the suspect isolates tested. The PCR technique was shown to provide complementary information in cases where the pathogenicitytest did not show clear symptoms, and to give additional information on the suspected occurrence of X. campestris pv. armoraciae or X. campestris pv. raphani (Xca/Xcr). Similarly, the pathogenicity test would be valuable when an indeterminate PCR resultappears. The risk of a final false-negative result on a seed lot is minimized by testing at least six suspect isolates per seed subsample, as instructed by ISTA Method 7-019. The use of a PCR technique is highly recommended as an alternative or complementary method for Xcc identification in seed health testing laboratories.